The objective of the National HIV Behavioral Surveillance System (NHBS) is to investigate HIV risk, testing, and prevention services in order to design and evaluate HIV prevention efforts in New York City and throughout the United States. The New York City Department of Health and Mental Hygiene (DOHMH) proposes to conduct an ongoing, cyclical, cross-sectional research study of HIV risk among populations with historically high risk of HIV infection to accomplish this objective. NHBS would include qualitative ethnographic research, quantitative survey research, and HIV and supplemental infectious disease testing of three high-risk populations between 2011 and 2015: men who have sex with men (MSM), injection drug users (IDU), and heterosexuals at increased risk for HIV infection (HET). DOHMH proposes to study MSM in 2011 and 2014, IDU in 2012 and 2015, and HRH in 2013. Additionally, DOHMH proposes to study transgender women concurrently with the study of MSM in 2011. The NHBS quantitative survey would include questions in four domains: demographics, HIV risk behaviors, HIV testing, and the use of HIV prevention services. DOHMH will sample members of the target population through venue-based (MSM cycles) and respondent-driven sampling (IDU and HET cycles). DOHMH will complete NHBS surveys with a minimum of 500 MSM and IDU during those respective cycles and 450 HET during that cycle, for a total minimum of 2,450 surveys over the five year project period. DOHMH will conduct HIV testing to estimate HIV prevalence (through Western Blot diagnostic testing) and HIV incidence (through detuned assay STARHS testing) of each target population. Additionally, DOHMH will conduct testing for hepatitis B, hepatitis C, herpes simplex virus-2, and syphilis during all study cycles. DOHMH will also survey 200 transgender women during the first grant year, and conduct all testing listed above (HIV, HBV, HCV, HSV2, and syphilis) all study participants. Throughout the NHBS research study, DOHMH will collaborate with community partners including the local HIV Prevention Planning Group, HIV Planning Council, and federally-funded community-based organizations. DOHMH will also collaborate with local researchers with knowledge of the target populations and with expertise in qualitative research methods to conduct formative qualitative research on the three target populations to inform and support the main data collection phase. Finally, DOHMH will conduct evaluations of the NHBS system to refine the methods of HIV behavioral surveillance and will conduct analyses of NHBS data to describe the target populations and to investigate specific research questions on HIV risk.